Studies On Laster Induced Formation Of Molecular Junctions And On Novel SERS-based Biosensor

Surface-enhanced Raman scattering (SERS) is a highly sensitive and selective tool for the identification of biological or chemical analytes based on Raman scattering. Its narrow, well-resolved bands, low SERS intensity of water and high stability make SERS widely used in material science, surface science, analytical chemistry,sensors,biological characterization and diagnostics. In this thesis, the interaction between molecules and metallic nanoparticles, and the novel and simple SERS based biosensor platforms were investigated using surface-enhanced Raman spectroscopy (SERS). The details are summarized as follows:1. Laser power dependence of p-aminothiophenol (PATP) adsorption on Au nanoparticles (NPs) was systematically investigated using surface-enhanced Raman spectroscopy in chapter two. Molecular junctions (MJs) were found to form between NPs with PATP as the bridge molecule with an external energy provided by the incident laser. The formation of MJs depends on the laser illumination time, the aggregation states of NPs and the surface coverage of PATP. Furthermore, the MJs formed showed reversibility to be affected by the laser power and the illuminated time.2. In chapter three, a ultrasensitive HIV-1 DNA detection assay based on the multilayer metal-molecule-metal nanojunctions (NJs) was developed using surface-enhanced Raman spectroscopy (SERS). Taking advantage of the hybridization between two complementary DNA strands, the Raman signal of their terminal tag molecules was significantly enhanced with the formation of the metal-molecule-metal NJs between Au nanoparticles (NPs) capped by them. A detection limit towards HIV-1 DNA sequence has been obtained as low as 10-19 M(~10-23 mol), which successfully realized a simple SERS based assay approaching single molecular detection level.3. In chapter four, we developed an electrostatic interaction based biosensor for the thrombin detection using surface-enhanced Raman spectroscopy (SERS). This method utilized the electrostatic interaction between capture (thrombin aptamer) and probe (crystal violet, CV) molecules. The specific interaction between thrombin and aptamer could weaken the electrostatic barrier effect from the negative charged aptamer SAMs to the diffusion process of the positive charged CV from the bulk solution to the Au nanoparticle surface. Therefore, the more the bounded thrombin, the more the CV molecules near the Au nanoparticle surface and the stronger the observed Raman signal of CV, provided the Raman detections were set at the same time point for each case. This procedure presented a high selectivity and a linear detection of thrombin in the range from 0.1 nM to 10 nM with a detection limit of ca. 20 pM, and realized the thrombin detection in human blood serum solution directly.